This application claims the priority of Japanese Patent Applications No. 2001-75999 filed on Mar. 16, 2001 which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to variable power operation control of an electronic endoscope system capable of observing an optical enlarged image using a moving lens and capable of forming an electronic enlarged image by signal processing.
2. Description of the Related Art
In recent years, in an electronic endoscope system or the like, a moving lens for variable power has been disposed in an objective lens system in a scope distal-end portion, and this moving lens has been driven by an actuator or the like, by which an image of a subject to be observed has been enlarged optically. This optically enlarged image is picked up by an image pick-up element such as a CCD (Charge Coupled Device), and various types of image processings are performed by a processor based on the output signal from the CCD, by which an enlarged image of a subject to be observed is displayed on a monitor. In such an optical variable power mechanism, an observed image can be enlarged up to about 70 to 100 times.
On the other hand, conventionally, the image obtained by the CCD is enlarged electronically by picture element interpolation processing etc. of an electronic variable power circuit. According to this, the optically enlarged image can be further enlarged and displayed on the monitor for observation.
In the above-described electronic endoscope system having a variable power function, it has been proposed a technology in which a common variable power switch provided, for example, in an endoscope operating section is used to operate optical variable power and electronic variable power in connection with each other. Specifically, after the variable power switch is operated to move the moving lens to an enlargement end (Near end) by optical variable power, the variable power is automatically shifted to electronic variable power to form a further enlarged image by signal processing. Thereby, a particular portion of an affected part etc. can be observed rapidly with a satisfactory magnification.
However, in the conventional optical variable power mechanism using the moving lens, the depth of field decreases with increasing enlargement ratio, which presents a problem in that, for example, for a subject to be observed having irregularities, there is a case where the whole of the subject in the depth direction cannot be displayed properly. This phenomenon will be described now with reference to FIGS. 7 and 8.
In FIG. 7, the left-hand side view shows a state in which when a movable lens 1 lies at the Far end, the proximal end, a subject to be observed 2 forms an image on a CCD image pick-up surface 3, and the right-hand side view shows an image formation state at the time when the moving lens 1 is moved to the Near side, the enlargement side. In FIG. 7, since the moving lens 1 is set at a position of distance 0, at the time of enlargement, the image pick-up surface 3 is drawn so as to be shifted rearward. Actually, the moving lens 1 moves forward. When the optical enlargement is not made as shown in the left-hand side view of FIG. 7, the focus is sharpened, for example, at a distance of 8 to 100 mm, and the depth of field is 92 mm. Whereas, when the optical enlargement is made as shown in the right-hand side view in FIG. 7, the focus is sharpened at a distance of 4 to 20 mm, and the depth of field is 16 mm.
FIG. 8 is an explanatory view of the depth of field. Taking the focal length of a lens 4 as f, the F number as FN, the allowable blur circle as xcex4, and the distance of subject to be observed as L, the rear depth of field Lr and the front depth of field Lf are expressed as follows:
Lr=(xcex4xc2x7FNxc2x7L2)/(f2xe2x88x92xcex4xc2x7FNxc2x7L)xe2x80x83xe2x80x83(1)
Lf=(xcex4xc2x7FNxc2x7L2)/(f2+xcex4xc2x7FNxc2x7L)xe2x80x83xe2x80x83(2)
The depth of field of this lens 4 is a value obtained by summing up the rear depth of field Lr and the front depth of field Lf, that is, Lr+Lf. The depth of focus is 2xcex4xc2x7FN.
The aforementioned depth of field explained in FIG. 7 is also the above-described value of Lr+Lf, and the range in which the focus is sharp is 92 mm at the Far end and 16 mm at the Near end. In the configuration of variable power objective optical system now used for an endoscope, the depth of field decreases as the image is enlarged. Therefore, in the case where a subject to be observed having irregularities is observed, the depth of field becomes shallow (short), so that a blur occurs somewhere in the depth direction. When the subject to be observed is caught in a state of shallow depth of field is enlarged electronically, the blur in the depth direction is also enlarged, which presents a problem in that the whole of the subject to be observed cannot be displayed and observed with high picture quality.
The present invention has been achieved to solve the above problems, and accordingly an object thereof is to provide an electronic endoscope system having a variable power function, which is capable of arbitrarily setting the depth of field at the time of shifting to electronic variable power to eliminate a blur in the depth direction of electronically enlarged image.
To attain the above object, an electronic endoscope system having a variable power function, comprising: an objective optical system for optically magnifying an image to be observed by using a variable power lens; an electronic variable power circuit for electronically magnifying an image obtained via an image pick-up element by signal processing; common variable power operating means for operating the optical variable power and electronic variable power; switching point setting means for setting a depth of field at the switching time between the optical variable power and electronic variable power at an arbitrary value; and a control circuit which continuously operates optical variable power and electronic variable power based on the operation of the variable power operating means, and controls the switching between optical variable power and electronic variable power with the arbitrary setting value of depth of field being a switching point. This control circuit sets the depth of field by changing it into the position of variable power lens.
Also, another invention is characterized in that an enlargement ratio, not a depth of field, is used as a control element for switching between optical variable power and electronic variable power, and when the enlargement ratio becomes an arbitrary setting value, transfer from optical enlargement to electronic enlargement is effected. Specifically, a change in depth of field can also be detected by a change in enlargement ratio, and the value of depth of field can be controlled by the value of enlargement ratio.
According to the above-described configuration, the control for transferring to electronic variable power is carried out by the set value of depth of field, for example, in a field depth preference mode, not in an ordinary mode in which electronic variable power is effected when the variable power lens moves to the Near end. In this field depth preference mode, if the value of depth of field at the time of transfer to electronic variable power is set by key operation on a control panel etc. of a processor, the position (for example, a1) of moving lens corresponding to the value of depth of field is calculated, and this lens position a1, is stored and held in a memory etc.
When operation is performed in the enlargement direction by using the variable power switch, optical variable power is first effected. If the enlargement operation is further performed after the moving lens has reached the position a1, the optical variable power operation is stopped, and subsequently electronic variable power is executed. Therefore, when electronic enlargement is made, an arbitrarily set depth of field is maintained. Therefore, even for a subject to be observed with a depth, an enlarged image in which the focus is sharp in a wide range can be displayed and observed.